If you can get a parent to heat the plastic bottle in a bowl of hot water, then put the wad of paper in the mouth of the bottle, the paper wad will get sucked in by itself. This is because as the bottle cools, so does the air inside of it. As the air cools inside the botle, it condenses and takes up less space, creating a void inside the bottle. therefore, more air is needed to fill the bottle. As more air is drawn into the bottle, the wad of paper will get sucked in with it.